blue roach

from The Collaborative International Dictionary of English v.0.48

Rudd \Rudd\, n. [See {Rud}, n.] (Zool.)
   A fresh-water European fish of the Carp family ({Leuciscus
   erythrophthalmus}). It is about the size and shape of the
   roach, but it has the dorsal fin farther back, a stouter
   body, and red irises. Called also {redeye}, {roud},
   {finscale}, and {shallow}. A blue variety is called
   {azurine}, or {blue roach}.
   [1913 Webster]